1. Field of the Invention
The present invention relates to a method for the preparation of pyrazine derivatives of the formula ##STR5## wherein R.sub.1 represents a hydroxyl group, a C.sub.1 -C.sub.6 alkoxyl group, or a group of the formula NR.sub.2 R.sub.3 in which both R.sub.2 and R.sub.3 are independently a hydrogen atom or a C.sub.1 -C.sub.6 alkyl group, or are linked together to form a saturated ring having five or six atoms and optionally containing other heteroatoms such as O, N, and S. Preferred ring systems so formed are piperidine, pyrrolidine, morpholine, piperazine, and thiazolidine. In particular, the method is useful for the preparation of 5-methyl-pyrazin-1-carboxylic-4-oxide acid (R.sub.1 =OH).
2. Description of the Prior Art
Compounds of formula I as above defined have been recognized as having hypolipoemic or hypoglycaemic activity as more clearly demonstrated in British Patent Specification No. 1,361,967.
The patent also discloses a method for preparing compounds of formula I by the oxidation of a compound of the formula: ##STR6## wherein R.sub.1 is as previously defined, by means of hydrogen peroxide. While this previously described process may be satisfactory for producing small quantities of pyrazine derivatives, the use of a dangerous oxidizing reagent such as hydrogen peroxide is not suitable for industrial scale production. Applicants have surprisingly found a novel and certain method for preparing compounds of formula I on a large scale without use of an oxidizing reagent.